This invention relates to a heat treating apparatus in which metals in various forms such as powders or rods are melted by gaseous plasmas.
Such a heat treating apparatus is conventionally known in which metals are melted with a gaseous plasma ejected from nozzles in the form of a plasma jet. However, molten metal in a cooling crucible of a heat treating apparatus making use of a single plasma jet assumes a funnel-shaped form and so generated ingots are a inhomogeneous structure with characteristic patterns. This inhomogeneity itself of ingots leads to a disadvantage of decreasing the mechanical strength of metallic material. On the other hand, when the metal to be melted includes non-metallic components, the non-metallic components in a molten pool are forced into the inner portion of the ingot by crystallization surfaces, which results in the contraction and split of the ingot and makes difficult the mechanical work up of the ingot.
This inhomogeneity in the ingot is moderated considerably by arranging a plurality of plasma jets around the central axis of the apparatus and effectuating sectionalized heating. This inhomogeneity is moderated futher by setting and fixing the plural plasma jets beforehand such that the jetting velocities of the plural plasma jets have components in the circumferential direction of the apparatus. In this case, the molten metal is caused to revolve around the axis of the apparatus by the kinetic energy of the plasma jets. However, if the sectionalized heating and the revolution of the molten metal are to be done effectively by the plural plasma jets, the positions and directions of the nozzles must be set precisely aforehand based on the analysis of the estimate of the flow pattern and the temperature distribution of the molten metal. Moreover, when the operating conditions of the heat treating apparatus vary according to the components of the raw metal and the requirement on the constitution of the ingot, the plural nozzles must be rearranged for an optimum condition.